a) 2^1994 - 2^1993 = 2^1993 x (2-1) = 2^1993 x 1 = 2^1993
b) 3^1994 + 6x3^1993 = 3 x 3^1993 + 6x3^1993 = 3^1993 x (3+6) = 3^1993 x 9 =
= 3^1993 x 3^2 = 3^1995
c) 2^1993 x 3^1994 - 3^1993 x 2^1994 = 2^1993 x 3^1993 x (3 - 2) = 2^1993 x 3^1993 x 1 = 2^1993 x 3^1993